okay I special cased it

vacuum_gambit.p8

@@ -368,7 +368,7 @@ function draw_gun_info(lbl,fgc,x,y,gun)
 end
 
 function vertmeter(x0,y0,x1,y1,val,maxval,cols)
- if (val <= 0) return
+ if (val <= 0 or maxval <= 0) return
  local h = y1-y0
  local px = -flr(-(h*val)\maxval)
  local ncols = #cols